Synthesis of hydrochar from jackfruit

ABSTRACT

A method of producing hydrochar from jackfruit peel biomass includes hydrothermal carbonization of jackfruit peel biomass by autoclaving at 150° C.-250 ° C. for about 3 hours to produce a hydrochar. The hydrochar can be activated by treatment with phosphoric acid (H3PO4), hydrogen peroxide (H2O2), or a combination thereof. The hydrochar produced according to the method is particularly effective at removing azo-dyes, and specifically methylene blue, from aqueous solutions such as industrial waste water.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 16/360,397,filed Mar. 21, 2019, pending.

BACKGROUND 1. Field

The disclosure of the present patent application relates to hydrochar(HC), and particularly to a jack fruit peel hydrochar (JFHC) for theadsorptive removal of methylene blue (MB), a cationic synthetic dye,from an aqueous environment.

2. Description of the Related Art

Dyes are used as coloring agents and may be classified on the basis oftheir chromophores. Both synthetic and natural dyes, together includingmore than 10,000 commercial dyes, are used in various fields, includingfood science, arts, textiles, and fashion.

Methylene blue (MB) is an azo dye, extensively used for dyeing andprinting applications across technological fields. In lowconcentrations, MB is non-hazardous; however, acute MB exposure cancause cyanosis, jaundice, Heinz body formation, vomiting, and tissuenecrosis in humans. Monitoring and limiting MB concentration inwastewater streams before discharging them to water reservoirs isessential in preventing such noxious effects.

Generally, used-dye contaminated wastewater treatment technologiesinclude processes based on advanced oxidation, biodegradation,ion-exchange, and adsorption. Water treatment technologies based onadsorption have advantages of operational simplicity, economicfeasibility and high efficiency. Activated carbon (AC) is a conventionaladsorbent used for sequestering pollutants from water. However,regeneration and slow desorption kinetics restrict wide range usage ofAC. Additionally, AC is commonly derived from non-renewable coal, and istherefore in finite supply.

Char produced from an abundantly available solid waste biomass—forexample, from plants, animals and humans—is an alternate material forincorporating into an adsorption-based waste management approach. Char,whether biochar (BC) or hydrochar (HC), produced from otherwise uselesssolid waste biomass, is a carbonaceous product having a wide range ofenergy and environmental applications. HC is typically generated byhydrothermal carbonization (HTC) of wet/dry waste biomass in a lowtemperature range of 150° C.-350° C. Relative to BC, HC has high oxygenfunctional groups content, but lower porosity and surface area.

Jackfruit (JF), Artocarpus heterophyllus, is widely grown in tropicalclimates. Usually, a mature JF weighs 10 kg-25 kg. A fibrous rind andunfertilized floral parts, comprising around 50% of the JF mass,contribute no economic or nutritional value and are usually discarded aswaste. The jack fruit peel (JFP) thereby presents a significant sourceof wasted biomass.

Accordingly, a method of synthesizing hydrochar from jackfruit solvingthe aforementioned problems is desired.

SUMMARY

A method of synthesizing jackfruit hydrochar (JFHC) from jackfruit peelincludes subjecting jackfruit peel to hydrothermal carbonization (HTC)to provide a JFHC. The step of HTC may be performed at a temperatureranging from about 150° C. to about 250° C. for a set reaction time ofabout 30 min to about 24 hours. The JFHC can be chemically activated.Activation of the JFHC may include treatment with phosphoric acid(H₃PO₄, PA) and/or hydrogen peroxide (H₂O₂, HP). JFHC produced accordingto the presently disclosed methods effectively adsorbs MB from anaqueous environment.

These and other features of the present teachings will become readilyapparent upon further review of the following specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reaction scheme for the development and chemical activationof JFHC@150/3.

FIG. 2 is a plot showing the Fourier transform infra-red (FT-IR) spectraof JFHC@150/3, JFHC@150/3_PA, and MB saturated JFHC@150/3_PA.

FIG. 3 is a plot showing XPS survey spectra of pristine and MB saturatedJFHC@150/3_PA.

FIGS. 4A-4B shows scanning electron microscopy (SEM) images of pristine(FIG. 4A) and MB saturated JFHC@150/3_PA (FIG. 4B).

FIGS. 5A-5B shows energy dispersive X-ray (EDX) spectroscopy spectra ofpristine (FIG. 5A) and MB saturated JFHC@150/3_PA (FIG. 5B).

FIG. 6 is a plot showing thermogravimetric (TGA-DTA) analysis ofJFHC@150/3_PA.

FIGS. 7 is a diagrammatic representation of methylene blue (MB)adsorption on JFHC@150/3_PA.

FIG. 8 is a plot showing the effect of initial pH (pH_(i)) on MBadsorption onto JFHC@150/3_A.

FIG. 9 is a plot showing the effect of JFHC@150/3_PA dose on MBadsorption.

FIG. 10 is a plot illustrating the effect of contact time on MBadsorption at varied concentrations onto JFHC@150/3_PA.

FIG. 11 is a plot illustrating equilibrium adsorption capacity versusequilibrium concentration at varied temperatures.

FIG. 12A is a plot presenting adsorption/desorption of MB fromJFHC@150/3_PA by various eluents.

FIG. 12B is a plot presenting the adsorption/desorption of MB fromJFHC@150/3_PA by HCOOH at varied concentrations.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of synthesizing jackfruit hydrochar (JFHC) from jackfruit peelincludes subjecting jackfruit peel to hydrothermal carbonization (HTC)to provide an initial JFHC. Preferably the jackfruit peel is dried andpulverized before being subjected to HTC. The method of synthesizingJFHC may further include an activation step to optimize the initial JFHCas an effective adsorbent for cations, such as methylene blue (MB), fromaqueous environments.

The step of HTC may be performed at a temperature ranging from about150° C. to about 300° C., e.g., 150° C. to about 250° C. for a setreaction time. The reaction time can range from about 30 min to about 24hours. According to an embodiment, the HTC is performed at a temperatureof about 150° C. for about 3 hours. Activation of the initial JFHC mayinclude treatment with an activating compound, such as phosphoric acid(H₃PO₄, PA), hydrogen peroxide (H₂O₂, HP), or both. Exemplary chemicalconditions for activating the initial JFHC can include treatment with0.1 N phosphoric acid (H₃PO₄, PA) or, alternatively, 10% hydrogenperoxide (H₂O₂, HP). The chemically activated JFHC sample can then beseparated using any suitable method, e.g., filtration or centrifugation.For example, filtration can be conducted using Whatman filter paper 41.JFHC produced according to the presently disclosed methods effectivelyadsorbs MB from an aqueous environment.

A method of removing MB from an aqueous environment can includecontacting the activated JFHC with the aqueous environment.

As used herein, the term “about” when modifying a numerical value shallmean within 10% of the modified numerical value.

As described herein, an exemplary JFHC sample exhibiting maximal MBremoval efficiency was prepared by subjecting jackfruit peel biomass tohydrothermal carbonization at 150° C. for 3 h to provide JFHC, andchemical activation of JFHC with 0.1N PA to provide an activated JFHC,referred to hereinafter as “JFHC@150/3_PA”. Fourier-transform infraredspectroscopy (FT-IR) analysis confirmed that phosphate (PO₄ ³⁻) groupswere covalently attached with hydroxyl (—OH) groups during chemicalactivation of the JFHC@150/3_PA. The adherence of PO₄ ³⁻ group withJFHC@150/3_PA during chemical activation was further confirmed by X-rayphotoelectron spectroscopy (XPS), which revealed the presence of aspectral peak at 133.7 eV, characteristic of P2p. After MB adsorption onJFHC@150/3_PA, as described herein, spectral peaks observed at 401 and163 eV, attributed to N1 s and S2p, confirmed successful adsorption ofMB on JFHC@150/3_PA. Morphologically, a surface of pristineJFHC@150/3_PA appeared uneven and porous prior to MB adsorption.Following MB adsorption, the surface of JFHC@150/3_PA appeared lessporous, presumably due to occupation of pores with MB molecules. A totalof 78% weight loss of the JFHC@150/3_PA sample for a temperature rangingfrom 30° C.-750° C. was observed during thermogravimetric analysis (seeFIG. 6).

Maximum MB adsorption (214.7 mg/g) on JFHC@150/3_PA was observed for aninitial pH (pH_(i)) of 7.24. The MB adsorption capacity decreased and %adsorption increased with an increase in JFHC@150/3_PA dose. The contacttime study at varied MB concentration C_(o) from 25 mg/L-100 mg/Lrevealed an increase in adsorption capacity from 80.8 mg/g to 261.6mg/g, while the equilibration time varied between 240 min (4 h) to 360min (6 h). The adsorption of MB for C_(o) in the range: 15 mg/L-150 mg/Ldecreased with increase in temperature for the temperature range 20°C.-50° C.

During the desorption study described in the following examples, acids(HCl, HCOOH, CH₃COOH) of 0.1 M concentration, base (NaOH) of 0.1 Mconcentration and solvents (CH₃OH, C₂H₅OH, CH₃COCH₃) were used to eluteMB from JFHC@150/3_PA samples. A maximum (40.4%) MB elution was observedwith 0.1 M HCOOH, and increased to 52.6%, with 10-folds (1.0 M) increasein HCOOH concentration.

EXAMPLE 1 Synthesis of Jackfruit Peel Hydrochar (JFHC)

Waste JFP was collected from a local vegetable market in Saudi Arabia,chopped with a knife into small pieces (˜1 cm cube), and dried at 60° C.for a week in an oven. The dried JFP was washed with deionized (D.I.)water to completely remove any impurities, such as dirt and dust. Thedried and rinsed JFP was again dried overnight at 60° C. and the driedJFP was manually crushed using a mortar and pestle. The uniformlycrushed JFP biomass was subjected to HTC in a 200 mLpolytetrafluoroethylene (PTFE) lined autoclave. In a typical HTCprocedure, a slurry of JFP biomass was first made by adding 75 mL D.I.water to 8 g JFP biomass, and then transferred to an HTC reactor. Thereactor was sealed and heated at 150° C. for 3 h in an oven and was thencooled at room temperature. The sample (JFHC@150/3) was collectedthrough filtration and washed several times with D.I. water to removeunwanted products generated during the HTC process. FIG. 1 schematicallyshows the method of synthesizing JFHC@150/3. Analogous embodiments ofthe present method were used to synthesize JFHC samples at 200° C.(JFHC@200/3) and 250° C. (JFHC@250/3).

EXAMPLE 2 Chemical Activation of Developed JFHC Samples

The developed JFHC samples (JFHC@150/3, JFHC@200/3 and JFHC@250/3) werechemically activated with phosphoric acid (0.1 N H₃PO₄; PA), hydrogenperoxide (10% H₂O₂; HP), and a phosphoric acid+hydrogen peroxide (0.1NH₃PO₄+10% H₂O₂: PA+HP) mixture. One gram of JFHC@150/3 was treatedseparately with either 50 mL PA (JFHC@150/3_PA), 50 mL HP(JFHC@150/3_HP), or 50 mL PA+HP (JFHC@150/3_PA_HP) with stirring by amagnetic stirrer at 200 rpm for an hour. The resulting chemicallyactivated samples were separated, e.g., through filtration, and washedseveral times with D.I. water until a neutral pH of the JFHC rinse waterwas achieved. All three samples were dried overnight at 80° C. in anoven. The same activation protocols for chemical activation wereperformed on the JFHC@200/3 and JFHC@250/3 samples. The nomenclature ofthe resulting synthesized JFHC samples is given in Table 1. FIG. 1illustrates the JFHC@150/3 activation with PA through covalent bondformation.

TABLE 1 Hydrothermal carbonization and chemical activation conditions,nomenclature, and MB adsorption on JFHC samples S4 sample selected fordetailed MB adsorption studies. HTC Conditions MB Temp Time adsorptionS. No. (° C.) (h) Chemical Treatment Nomenclature (%) S1 150 3 UntreatedJFHC@150/3 93.3 S2 200 3 Untreated JFHC@200/3 92.4 S3 250 3 UntreatedJFHC@250/3 92.4 S4 150 3 0.1N H₃PO₄ JFHC@150/3_PA 99.5 S5 200 3 0.1NH₃PO₄ JFHC@200/3_PA 98.5 S6 250 3 0.1N H₃PO₄ JFHC@250/3_PA 98.6 S7 150 310% H₂O₂ JFHC@150/3_HP 99.0 S8 200 3 10% H₂O₂ JFHC@200/3_HP 98.6 S9 2503 10% H₂O₂ JFHC@250/3_HP 98.8 S10 150 3 0.1N H₃PO₄ + 10% H₂O₂JFHC@150/3_PA_HP 99.1 S11 200 3 0.1N H₃PO₄ + 10% H₂O₂ JFHC@250/3_PA_HP98.8 S12 250 3 0.1N H₃PO₄ + 10% H₂O₂ JFHC@250/3_PA_HP 99.1

EXAMPLE 3 Characterization of Developed and Chemically Activated JFHCSamples, and Presumed MB Adsorption Mechanism

The functional groups present on the pristine JFHC@150/3 andJFHC@150/3_PA samples and involved during MB adsorption on JFHC@150/3_PAwere detected by FT-IR (Nicolet 6700, Thermo Scientific, USA)spectroscopic analysis, as illustrated in FIG. 2. A band at 3443 cm⁻¹was attributed to hydroxyl (—OH) group stretching vibrations (Wang etal., 2017). Two adjacent bands at 2827 cm⁻¹ and 2928 cm⁻¹ wereattributed to symmetric and asymmetric vibrations of C—H groups (Wang etal., 2017). A band at 1733 cm⁻¹ was attributed to carbonyl (C═O) groupstretching vibrations in ester and acetyl linkages in hemicellulose andlignin. Bands at 1622 cm⁻¹ and 1519 cm⁻¹ were associated with thearomatic ring present in lignin. The bands at 1053 cm⁻¹ and 1159 cm⁻¹were associated with C—O—C stretching vibrations in cellulose. Afterchemical activation of JFHC@150/3 with PA, a band in range: 973cm⁻¹-1100 cm⁻¹, characteristic of phosphate (PO₄ ³⁻) group appeared(Roguska et al., 2011). However, this band was overlapped with signalfrom C—O—C groups, confirmed by a decrease in band size. Additionally,PO₄ ³⁻ groups were covalently attached with —OH groups present onJFHC@150/3 during chemical activation, confirmed by a decrease in bandsize due to dehydration. After MB adsorption on JFHC@150/3_PA, the bandsat 1059 cm⁻¹ and 3443 cm⁻¹ were shifted to 1040 cm⁻¹ and 3431 cm⁻¹ witha decrease in their respective sizes.

The chemical composition of pristine and MB saturated JFHC@150/3_PA werecharacterized by XPS (Joel JPS-9200, Japan) analysis. FIG. 3 shows thespectrum resulting from pristine JFHC@150/3_PA, with three peaks at 531eV, 284.6 eV and 133.7 eV, attributable to O1s, C1s, and P2p,respectively. Two new peaks at 401 eV and 163 eV attributed to N1s andS2p appear in the spectrum of MB saturated JFHC@150/3_PA. The appearanceof N1s and S2p peaks in the MB saturated JFHC@150/3_PA spectrum isconsistent with MB adsorption onto the JFHC@150/3_PA surface.

The morphology and elemental content of pristine and MB saturatedJFHC@150/3_PA were determined by scanning electron microscopy (SEM: Nova200 NanoLab, FEI, USA) coupled with energy-dispersive X-ray (EDX: AMETEKNova 200) spectroscopic analysis. FIG. 4A shows an uneven and irregularpristine JFHC@150/3_PA surface, with evident pores. After MB adsorption,the JFHC@150/3_PA surface appears smoother with less apparent pores(FIG. 4B), presumably due to the formation of an MB film over thesurface. The elemental analysis spectrum and elemental mapping image ofJFHC@150/3_PA (FIG. 5A) shows traces of phosphorus, confirmingsuccessful chemical modification of JFHC@150/3 surface with PA. After MBadsorption on JFHC@150/3_PA, traces of nitrogen and sulfur were presentin the elemental analysis spectrum, confirming attachment of MB to theJFHC@150/3_PA surface (FIG. 5B).

Thermogravimetric analysis of JFHC@150/3_PA was performed (TGA-DTA: Q500TGA, USA) at temperatures ranging from 30° C.-750° C. under N₂atmosphere. FIG. 6 shows 4% weight loss as temperature increases from30° C.-100° C., presumably due to evaporation of physically adsorbedwater molecules from the JFHC@150/3_PA. A drastic 60% weight loss ofJFHC@150/3_PA occurred between 250° C. and 400° C., presumably due tothe decomposition of cellulose, hemicellulose and lignin typical ofplant biomass. Furthermore, 14% weight loss occurred betweentemperatures ranging from 400° C. to 750° C., presumably due todegradation of lignin.

FIG. 7 diagrammatically shows possible mechanisms for adsorption of MBon JFHC@150/3_PA, including formation of hydrogen bonds between —OHgroups present on JFHC@150/3_PA and dimethylamino (—N(CH₃)₂) groups ofMB dye, electrostatic interactions between the electron rich oxygenatoms on JFHC@150/3_PA and MB cations, and π-π stacking interactionsbetween the aromatic rings of JFHC@150/3_PA and MB dye.

EXAMPLE 4 Adsorption Experiments and Results

Preliminary studies were carried out to evaluate performance among thepristine and chemically activated JFHC samples for maximum MB removalefficiency. Batch scale adsorption experiments were carried out in 100mL Erlenmeyer flasks, containing 25 mL MB solution of initialconcentration (C_(o)). 20 mg/L was equilibrated with 0.01 g eachpristine or chemically activated JFHC sample, under shaking conditionsat 80 rpm for 24 h. Once equilibrium was reached, solid (JFHC sample)and solution (MB solution) phases were separated through filtration andthe residual MB concentration was analyzed by UV-visible spectrometry(Thermo Scientific Evolution 600, UK) at a maximum wave length (λ_(max))of 665 nm. The adsorption of MB on JFHC was calculated as:

$\begin{matrix}{{{Adsorption}\mspace{14mu} (\%)} = {\frac{C_{o} - C_{e}}{C_{o}} \times 100}} & (1)\end{matrix}$

The observed MB adsorptions (in %) for each JFHC sample is provided inTable 1 (under Example 2). The effect of variables viz., pH, contacttime (t), temperature (T), dose (m), initial concentration (C_(o)) on MBadsorption onto JFHC@150/3_PA (sample with maximum (99.5%) MB removal)were further studied and MB adsorption capacities at equilibrium and atany time t were calculated as:

$\begin{matrix}{{{Adsorption}\mspace{14mu} {capacity}{\mspace{11mu} \;}{at}\mspace{20mu} {equilibrium}\mspace{14mu} \left( {q_{e},{{mg}\text{/}g}} \right)} = {\left( {C_{o} - C_{e}} \right) \times \frac{V}{m}}} & (2) \\{{{Adsorption}\mspace{14mu} {capacity}\mspace{14mu} {at}\mspace{14mu} {time}\mspace{14mu} t\mspace{14mu} \left( {q_{t},{{mg}\text{/}g}} \right)} = {\left( {C_{o} - C_{t}} \right) \times \frac{V}{m}}} & (3)\end{matrix}$

The adsorption of MB at C_(o): 50 mg/L on JFHC@150/3_PA as a function ofpH_(i) is illustrated in FIG. 8. The MB adsorption capacity was 74 mg/gat pH_(i): 2.7, sharply increased to 210.4 mg/g at pH_(i): 5, thenslowly increased, reaching a measured maximum of 214.7 mg/g at pH_(i):7.2.

The adsorption of MB at C_(o): 50 mg/L was studied by varyingJFHC@150/3_PA dose, as illustrated in FIG. 9. For doses in the range of0.01 g-0.1 g, the MB adsorption capacity decreased from 195.3 mg/g to24.9 mg/g, while the percentage (%) adsorption increased from 78% to99.7%.

The adsorption of MB on JFHC@150/3_PA as a function of contact time wasstudied at varied MB C_(o) ranging from 25 mg/L-100 mg/L, as illustratedin FIG. 10. For an initial 30 minutes of contact time, a sharp increasein MB adsorption was observed. Thereafter, the adsorption processapproached an equilibrium. The equilibration time for the studied C_(o)values varied from 360 min (6 h) to 480 min (8 h).

FIG. 11 shows equilibrium concentration (C_(e)) versus adsorptioncapacity at equilibrium (q_(e)) for MB adsorption on JFHC@150/3__PA atvaried temperatures. The MB adsorption on JFHC@150/3_PA decreased withincrease in temperature, consistent with exothermic MB adsorption.

EXAMPLE 5 Desorption Experiments and Results

The regeneration potential of JFHC@150/3_PA was tested through batchscale desorption experiments. The MB saturated JFHC@150/3_PA samplesdescribed in Example 4 were washed several times with D.I. water tocompletely remove unadsorbed M.B. Thereafter, the saturatedJFHC@150/3_PA samples were treated with one of several eluents chosenfrom a group of solvents and 0.1 M base or acid solutions. The amount ofMB desorbed was calculated as:

$\begin{matrix}{{{Desorption}\mspace{14mu} (\%)} = {\frac{{Concentration}{\mspace{11mu} \;}{of}\mspace{14mu} {MB}\mspace{14mu} {desorbed}\mspace{14mu} {by}\mspace{14mu} {eluent}}{\begin{matrix}{{{Initial}{\mspace{11mu} \;}{concentration}\mspace{14mu} {of}\mspace{14mu} {MB}\mspace{14mu} {adsorbed}\mspace{14mu} {on}}\mspace{14mu}} \\{{{JFHC}@150}/3{\_ PA}}\end{matrix}} \times 100}} & (4)\end{matrix}$

FIG. 12A shows maximum (40.4%) MB desorption was observed followingtreatment with 0.1 M HCOOH. Among the other eluents tested, MBdesorption percentage followed the trend: 0.1M CH₃COOH>0.1MHCl>CH₃OH>CH₃COCH₃>C₂H₅OH>0.1M NaOH. The effect of HCOOH concentrationon MB recovery from the saturated JFHC@150/3_PA samples is illustratedin FIG. 12B. The MB desorption increased with increasing HCOOHconcentration from 0.05 M to 1.0 M, achieving a maximum desorption of52.6%.

It is to be understood that the method of synthesizing hydrochar fromjackfruit is not limited to the specific embodiments described above,but encompasses any and all embodiments within the scope of the genericlanguage of the following claims enabled by the embodiments describedherein, or otherwise shown in the drawings or described above in termssufficient to enable one of ordinary skill in the art to make and usethe claimed subject matter.

1-17. (canceled)
 18. A method of removing methylene blue from an aqueousenvironment, comprising contacting the hydrochar of jackfruit peel withthe aqueous environment, wherein the hydrochar of jackfruit peel isproduced by steps comprising: adding a jackfruit peel biomass to aliquid carrier; subjecting the jackfruit peel biomass in the liquidcarrier to hydrothermal carbonization to provide a hydrochar, thehydrothermal carbonization comprising heating the jackfruit peel biomassin the liquid carrier to a temperature ranging from 150° C. to 250° C.for a period of time of 3 hours to provide the hydrochar; and separatingthe hydrochar from the liquid carrier.
 19. The method of claim 1,wherein the hydrochar is incubated in the aqueous environment for about24 hours.